1. Field of the Invention
An embodiment of the invention relates to an RF circuit switching circuit, which may include an RF circuit switching circuit which is used in a radio characteristic test for communication apparatus and is small, excellent in transmission characteristics and easy in maintenance and repair.
2. Description of the Related Art
In a radio characteristic test for a communication apparatus, it needs to conduct an efficient test on each of a large number of communication routes. For this reason, an RF signal circuit is sequentially switched using a radio frequency (RF) matrix switch.
A technique is known in which any one of radio frequency switches is turned on or off in a microwave communication apparatus (refer to Japanese Patent Laid-Open No. 60-247392). A technique is known in which a plurality of transfer switches is used in a circuit distributing circuit having a plurality of input and output circuits (refer to Japanese Patent Laid-Open No. 07-336128). A technique is known in which the transfer switches of a feeder circuit for selecting a plurality of element antennas are decreased in number in an array antenna (refer to Japanese Patent Laid-Open No. 62-160826).
FIGS. 6 and 7 show the structure of an RF circuit (or line) switching circuit (hereinafter, referred to as “switching circuit”) as a background of the present invention. The switching circuit is used for testing a circuit (4×4 circuit) comprising four input RF circuits and four output RF circuits. FIG. 6 shows an example in which a relay switch is used, and FIG. 7 shows an example in which a circuit selector is used.
To form the switching circuit shown in FIG. 6, eight switches (hereinafter, referred to as 6-1 switch) are needed for switching between six inputs (or outputs) and one output (or input). To form the switching circuit, twenty four internal wirings are needed in total, because four wirings are needed for input, sixteen wirings for connecting between the 6-1 switches, and four wirings for output. A control circuit (not shown) controls the eight 6-1 switches. Then, connections are switched between four input RF circuits (not shown) connected to four input terminals (IN1 to IN4) and four output RF circuits (not shown) connected to four output terminals (OUT1 to OUT4).
To form the switching circuit shown in FIG. 7, twenty four 24 circuit selectors (SPDT switches) are needed. To form the switching circuit, forty internal wirings are needed in total, because four wirings are needed for input, thirty two wirings for connecting between the SPDT switches, and four wirings for output. A control circuit (not shown) controls the twenty four SPDT switches. Then, connections are switched between four input RF circuits and four output RF circuits, as is the case with FIG. 6.
According to our study, the switching circuits cause various problems, since the size of the switching circuit is so large as described above.
That is, a large number of internal wirings comprises big waveguides or big coaxial cables, so that a housing for storing the switching circuits is increased in size. A large number of measuring instruments is used in a radio characteristic test, so that a large housing makes it inconvenient to place the switching circuits. The radio characteristic test needs a better transmission characteristic. However, in the example in FIG. 7, the connections of the switches and the internal wirings are increased in number, so that transmission characteristics is degraded in the switching circuit. The number of the internal wirings in the switching circuit is large, so that it becomes difficult to perform a daily maintenance and a repair at the time of failure. In addition, the 6-1 switch switches and SPDT switches are expensive, so that the switching circuit is costly.
One aspect of an object of the present invention is to provide an RF circuit switching circuit which is comparatively small, excellent in transmission characteristics and easy in maintenance and repair.